I don't get how being a member of a club makes you immune to prosecution and all non-members are ripe for the pickin. I'm not familiar with many US laws but that seems pretty weird... Was there an attempt at getting an injunction or did the FSC broker this sweetheart deal to encourage webmasters (most likely by the hundreds) to sign up.
On a side note, if I was a US webmaster I'd already be signed up for no other reason than to support a group that was fighting for my industry.